本刊英文版2010年53卷第12期摘要(英文)

A quasi-human algorithm for solving the three-dimensional rectangular packing problem HE Kun&HUANG WenQi Abstract Based on the concept of maximal rectangular space that can be filled at current time and the siege warfare tactics,we make several critical improvements on the quasi-human caving-degree approach to get a     

Effect of the silicon powder content on the properties of Al_2O_3-SiC-Me composites

By means of transient plastic phase process,the Al2O3-SiC-Me composites were produced throungh adding metal aluminium and silicon-powder to Al2O3-SiC materials.Under the condition of the same content of silicon and aluminium mixed-powder,the effect of silicon powder addition on properties of Al2O3-SiC-Me composites was studied by means of XRD and EPMA analyses in the temperature range of 300°C-1600°C.The results indicated that the content of metal phase in the sample at 1600°C increases with increasing silicon powder content.At the same time,when the temperature is lower than 1100°C,the strength of samples gradually increases with increasing temperature.However when the temperature is higher than 11000°C,the strength of samples gradually decreases with increasing temperature,and this change is very small.The results also indicated that at the same sintering temperature,the sample with 6%silicon powder has the maximum strength.     

Dielectric properties of BST/MZO ceramic composites

Ba0.6Sr0.4TiO3/Mg1-xZnxO(MZO,x=0,0.05,0.10,0.15 and 0.20) ceramic composites were prepared by traditional ceramic processing.The crystal structure,fracture surface morphology,and dielectric properties were investigated.The samples with x=0,0.05 and 0.10 exhibited favorable sintering behavior,and homogeneous diphase microstructure was obtained. Nevertheless,the microstructure of the samples with x=0.15 and 0.20 was inhomogeneous and abnormal grain growth could be observed,and the abnormal grain growth induced the degradation of dielectric strength.The sample with x=0.10 has relatively low dielectric loss(1.26×10-3) and the optimal FOM value(about 174) .     

Microstructure and texture evolution during warm compression of the magnesium alloy AZ31

The evolution of the microstructure and texture with strain during compression at 150℃of the magnesium alloy AZ31 has been investigated using the electron backscattered diffraction(EBSD)technique.The initial samples were chosen to have a strong basal plane texture with the crystal c-axes perpendicular to the compression direction.The EBSD data provide evidence concerning the relative activity of both{10-12}extension twinning and slip,and suggest that non-basalc+a slip is important in samples deformed to a strain of more than 0.2.The relative contributions of the twinning and the slip during deformation have been discussed based on the results above.     

Understanding of the influence of process parameters on the heat transfer behavior at the metal/die interface in high pressure die casting process

The current paper focuses on the influence of the process parameters on the peak values of the interfacial heat transfer coefficient(IHTC)at metal/die interface during high pressure die casting(HPDC)process.A"step shape"casting and AM50 alloy were used during the experiment.The IHTC was determined by solving the inverse thermal problem based on the measured temperature inside the die.Results show that the initial die surface temperature(IDST,TDI)has a dominant influence while the casting pressure and fast shot velocity have a secondary influence on the IHTC peak values.By curve fitting,it was found that the IHTC peak value(hmax)changes as a function of the IDST in a manner of hmax=e αTγ DI .Such relationship between the IHTC peak value and the IDST can also be found when the casting alloy is ADC12,indicating that this phenomenon is a common characteristic in the HPDC process.     

Performance of an activated carbon made from waste palm shell in simultaneous adsorption of SO_x and NO_x of flue gas at low temperature

This study examined the individual and simultaneous adsorption of SOx(SO2)and NOx(NO-NO2)on activated carbon prepared from waste palm shell.The adsorption process was examined in a fixed bed reactor at low temperatures(100 300°C).For individual adsorption without any catalytic activation,SOx showed good adsorption whereas NOx was very much poor.In the simultaneous adsorption of SOx and NOx,SOx showed greater adsorption affinity than NOx.For palm shell activated carbon(PSAC)impregnated with metal catalyst(Ni and Ce)the concentration adsorbed profile showed that the amount of SOx adsorbed decreased regularly,while the amount of the adsorbed NOx increased irregularly.The properties of the pure and impregnated PSAC were analyzed by BET,SEM and EDX.These investigations indicated that PSAC impregnated with metal catalyst is the determining factor in the adsorption of SOx and NOx simultaneously.     

Effect of Cu seed on the synthesis and characterization of FeCo alloy nano-particles by using polyol method

Fine metal particles with uniform shape,narrow size distribution and high purity are increasingly needed for specific uses in high tech industrial application.We report the direct chemical synthesis of FeCo alloy particles using the mixture of FeCl2·4H2O,Co(Ac) 2·4H2O(Ac:acetate) and NaOH in ethylene glycol,and then obtained FeCo alloy particles better dispersed by adding the polyvinylpyrrolidone(PVP) and also the size could be controlled by adding copper.The prepared nano-particles were characterized using FESEM,XRD and VSM.The mean diameter of these particles was varied in the range of submicrometer to nanometer with metal-ion concentration.FeCo particles showed the typical soft magnetic properties.     

Nonlinear dynamics of angle-ply composite laminated thin plate with third-order shear deformation

An asymptotic perturbation method is presented based on the Fourier expansion and temporal rescaling to investigate the nonlinear oscillations and chaotic dynamics of a simply supported angle-ply composite laminated rectangular thin plate with parametric and external excitations. According to the Reddy’s third-order plate theory, the governing equations of motion for the angle-ply composite laminated rectangular thin plate are derived by using the Hamilton’s principle. Then, the Galerkin procedure is applie...     

Preparation and properties of multi-wall carbon nanotube/SiC composites by aqueous tape casting

MWCNTS/SiC composites were fabricated by aqueous tape casting.High solid content(50 vol%) SiC slurries with sintering additives and multi-wall carbon nanotubes(MWCNTs) as reinforcements were prepared using Tetramethylammonium hydroxide as the dispersant.The stability of MWCNTs/SiC slurries was studied and characterized in terms of zeta potential and rheology measurements.The relative density of the composite was about 98%after hot-pressing at 1850°C(at 25 MPa in Ar for 30 min) .The hardness of the composites decreased with the increase in MWCNTs content.The flexural strength and the fracture toughness were 742.17 MPa and 4.63 MPa·m 1/2,respectively when the MWCNTs content was 0.25 wt%.Further increase in MWCNTs content to 0.50 wt%did not lead to the increase in mechanical properties.Most of MWCNTs were found to be located at SiC grain boundaries and the pull out of the MWCNTs was observed.     

Effect of one-step aging on microstructure and properties of a novel Al-Zn-Mg-Cu-Zr alloy

The effect of one-step aging temper on the mechanical properties,electrical conductivity and the microstructure of a novel Al-7.5Zn-1.6Mg-1.4Cu-0.12Zr alloy has been investigated.The results indicated that with elevating the aging temperature from 100°C to 160°C,the aging response rate was greatly accelerated,and the UTS at peak aging condition decreased,while the corresponding TYS increased.However,the electrical conductivity of the alloy became higher.After aging for 24 h at 120°C,the peak UTS and TYS values were achieved as 591 MPa and 541 MPa,respectively;but the alloy achieved a lower conductivity,20.4 MS/m.When T6 temper was performed at 140°C for 14 h,the UTS decreased only by 1%of the former,whereas the TYS and the electrical conductivity increased obviously,which were up to 559 MPa and 22.6 MS/m,respectively.The major strengthening precipitates of the peak-aged alloy were GP zones andη′phase.The precipitates in both the matrix and the grain boundary became coarser with rising aging temperature.There were obvious PFZs along the grain boundary both in T6 conditions aged at 140°C and 160°C.     

Effects of Ti,Al and Hf on niobium silcides formation in the Nb-Si in situ composites

The effects of alloying elements Ti,Al and Hf on niobium silicides formation in the Nb-Si in situ composites have been investigated by scanning electron microscopy(SEM) ,X-ray diffraction(XRD) and transmission electron microscopy(TEM) .The binary,ternary and multicomponent alloys have been fabricated by vacuum non-consumable arc melting method.The results show that Ti tends to stabilize Nb3Si phase,while Al promotes the direct formation ofβ-Nb5Si3 phase with a tetrahedral D8m structure.Exceptionally,it seems that Hf is beneficial to the formation ofγ-Nb5Si3 phase with a hexangular D88 structure.For the multicomponent Nb-Si in situ composites,the cooperative effects of different elements on niobium silicides formation basically maintain the character of ternary system.     

Optimization of the process for preparing Al-doped ZnO thin films by sol-gel method

Transparent and conducting Al-doped ZnO thin films with c-axis-preferred orientation were prepared on glass substrate via sol-gel route.The physical and chemical changes during thermal treatment were analyzed by TG-DSC spectra and the crystallization quality was characterized by XRD patterns.The optimized preheating and post-heating temperatures were determined at～420°C and～530°C,respectively.From thermodynamic and kinetics views,we investigated the mechanism of orientation growth with(002) plane parallel to the substrates.The surface morphologies of the films,post-heated at 420°C,450°C,530°C and 550°C,respectively,were observed by SEM micrographs.The film post-heated at 530°C shows a homogenous dense microstructure and exhibits the minimum sheet resistance of 140Ω/Sq.The visible optical transmittance of all the films is beyond 90%.In addition,the annealing treatment in vacuum can contribute greatly to the electrical conductivity.     

Dielectric tunable properties of BaTi_4O_9-doped Ba_(0.6)Sr_(0.4)TiO_3 microwave composite ceramics

BaTi4O9-doped Ba0.6Sr0.4TiO3(BST) composite ceramics were prepared by the conventional solid-state reaction and their structure,dielectric nonlinear characteristics and microwave dielectric properties were investigated.The secondary phase of the orthorhombic structure Ba4Ti13O30 is formed among BST composite ceramics with the increase of BaTi4O9.At the same time,a duplex or bimodal grains size distribution shows fine grains in a coarse grain matrix.The degree of frequency dispersion of dielectric permittivity below Tm is increased initially and then decreased with respect to BaTi4O9.As the BaTi4O9 content increases,the tunability of composite ceramics decreases,while the Q value increases.Interestingly,70 wt%BaTi4O9-doped BST has a tunability～4.0%(under 30 kV/cm biasing) versus a permittivity～68 and quality factor ～134.1(at～3.2 GHz) .     

Study on internal quantum efficiency of blue InGaN multiple-quantum-well with an InGaN underneath layer

Blue InGaN multiple-quantum-well (MQW) samples with different InxGa1-xN (x=0.01-0.04) underneath layers (ULs) were grown by metal organic vapor phase epitaxy (MOVPE). Temperature dependent photoluminescence showed that the InGaN UL can improve the internal quantum efficiency (IQE) of MQW effectively due to strain release. And a maximum IQE of 50% was obtained when the thickness and In content of the InGaN UL were 60 nm and 0.01, respectively. Furthermore, the larger In content or thickness of the InGaN UL m...     

Analysis of junction temperatures in high-power GaN-based LEDs

We presented the analysis of the incomplete conduction in bonding medium in high power GaN-based light-emitting diode (LED) packages. A numerical study was carried out with parametric model to understand the junction temperature variation due to bonding medium defects. Transient thermal measurement was performed to evaluate LED’s junction temperature. Thermal resistance from chip to lead frame was 20 K/W in our sample LED. It was suggested that only 60% of the surface area of the bonding medium was involved...     

Examination of dynamic recrystallization during compression of AZ31 magnesium

This study aimed to investigate dynamic recrystallization(DRX)behavior during compression of magnesium alloy AZ31. Cylinder samples were cut from the extruded rod and hot rolled sheet AZ31 for compression test.The samples were compressed using a Gleeble 1500D at a temperature of 300℃and a strain rate of 0.01 s-1.Grain orientations and misorientation angles across grain boundaries for the tested samples were obtained by using electron backscatter diffraction(EBSD)technique.The results showed that strong basal texture was observed after 50%compression(ε=0.69)on both the extruded and hot rolled samples,which have different initial textures.It was observed that with increased strain,DRX grains gradually rotated to basal orientation,and grain boundaries with misorientation angle of near 30°was formed in the samples.At the strain of 0.69,a high fraction of high-angle(60°)boundaries was present in the extruded sample,whereas almost no high angle boundaries were observed in the hot rolled sheet sample.     

Complex dynamics of functionally graded plates with thermal load in 1:2 internal resonance

Complex dynamics of the simply-supported functionally graded (FG) rectangular plates with thermal load is investigated. Based on Reddy’s third-order shear deformation theory and the von Karman nonlinear strain-displacement relations, ordinary differential equations (ODEs) of the plate’s transversal oscillation are derived by using Hamilton’s principle and Galerkin’s approach. Solutions’ classification of the equations in 1:2 internal resonance is analyzed. Particular results of a simply- supported aluminum-...     

Inducing effect of Pb(Zr_(0.4)Ti_(0.6))O_3 thin film derived by different processes in BiFeO_3/Pb(Zr_(0.4)Ti_(0.6))O_3 multilayer capacitor at room temperature

BiFeO3/PZT multilayer capacitor was prepared on Pt(100) /Ti/SiO2/Si(100) substrate.PZT buffer layer was derived by MOCVD method(label:PZT1) and sputtering method(label:PZT2) respectively.XRD analysis indicated that high(110) orientation of BFO in the BFO/PZT1 structure was achieved.SEM analysis indicated a better microstructure in the BFO/PZT1 structure compared with BFO/PZT2.The remnant polarization of the BFO/PZT1 was 82.5μC/cm2 at an applied voltage of 8 V,compared with that of 25.2μC/cm2 in the BFO/PZT 2 structure.The BFO/PZT1 multilayer exhibited little polarization fatigue(1.5%) upon 1×101 0switching cycles,at an applied voltage of 4 V.The leakage current density was about 2×10-7A/cm 2 at an applied voltage 4 V,in the BFO/PZT1 capacitor.All the results indicated that PZT can act as an inducing layer to the BFO and the MOCVD derived PZT has more inducing effect to the BFO thin film at room temperature.     

加工时间离散可控作业车间调度问题分解方法

给出了加工时间离散可控的作业车间调度问题（job-shop scheduling problem with discretely controllable processing times,JSP-DCPT）基于析取图的模型及其数学描述.提出一种三步分解方法,使得JSP-DCPT可以通过求解一个作业车间调度问题（job-shop scheduling problem,JSP）以及一系列离散时间-成本权衡问题得到解决.为简化分解方法,引入时间-成本相平面描述离散时间-成本权衡问题的权衡点,并详细阐释了一种基于极限模式的集合支配理论以确定用于消减JSP-DCPT分解所得离散时间-成本权衡问题的一个上界.随后提出一种基于极限模式的集合支配分解算法EMSDDA（extreme mode-based set dominant decomposition algorithm）.基于JSP标准算例FT10构造了测试算例JSPDCPT_FT10,实验仿真验证了提出的理论及分解方法的有效性.     

Improvement of warm formability of Al-Mg sheet alloys containing coarse second-phase particles

Several alloying elements involving Zr,Cu,Zn and Sc were added to Al-Mg sheet alloys in order to obtain an excellent combination of high strength and good high-temperature formability.Microstructural examination showed that coarse intermetallic particles were formed in the microstructure and their amounts changed with variations of the alloying elements. During warm rolling of thermomechanical treatments prior to warm deformation,the coarse particles initiated cracks,decreasing the warm formability.For healing the crack damage and further improving the warm formability,a process of hot isothermal press was developed and optimized to the sheet alloys.With this process,the biaxial stretch formability at 350°C was improved by 22%for an aluminum alloy containing a large amount of coarse particles.